The accuracy of beamforming weighting vectors is crucial to the performance of a wireless communications network employing a beamforming technique. A base transceiver station (BTS) computes beamforming weighting vectors based on downlink channel characteristics of the communication channel between the BTS and a mobile station (MS). The BTS obtains the downlink channel characteristics by requesting the MS or a customer premises equipment (CPE) to send training symbols through the communication channel in the uplink direction.
Once the BTS receives the training symbols, it extracts channel information about the downlink channel to compute beamforming weighting vectors. Channel information includes uplink channel quality information (CQI), carrier-to-interference-plus-noise ratio (CINR), Doppler frequency, Received Signal Strength Indication (RSSI), etc. Training symbols can be sent in the same format as uplink data or in a special uplink sounding format. Training symbols sent in the sounding signal format have better efficiency and are called sounding signals.
A communication channel in a wireless communications network has a fixed amount of radio bandwidth. Sending training symbols consumes radio resources and thus reduces the radio bandwidth reserved for sending data. Therefore, it is essential that a network should reduce overhead incurred as a result of training symbol transmission.
One way to deal with the issue related to radio resource consumption is to reduce the number of training symbol transmissions while providing channel information to the BTS. This could be effective because the data transmitted by the MS carries channel information similar to that carried by training symbols. If the BTS extracts channel information from the data transmitted by the MS, it will be reduce the needs for the BTS to transmit additional training symbol. In other words, the MS will need to send training symbols to the BTS only when there is no uplink data traffic.
Embodiments of the present invention disclose a scheduling algorithm that allocates transmission slots for uplink sounding signals efficiently.